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VOL. 72 (4), 629-642, 2006 PROTEIN PROCESSING IN PLASMODIUM FALCIPARUM?

shown by the bifunctional enzyme is ten times lower than that of
the monofunctional domain 6PGL (21), demonstrating its low
efficiency for 6-phosphogluconolactone hydrolysis. Moreover,
from a structural standpoint, it has also been questioned whether
the bifunctional protein is more efficient in producing NADPH
than two separate enzymes (21). NADPH is also the co-substrate of
Plasmodium glutathione reductase and thioredoxin reductase
enzymes that protects against oxidative stress caused mainly by
digestion of host cell haemoglobin at the late ring-early trophozoite
stage (35). Thus, different NADPH efficiencies could be required
at different developmental stages with particular specialization by
the bifunctional protein (21). Another explanation of this apparent
processing, is the genome economy shown by the small Plasmodium
genome containing a proportionally high number of genes compared
to similar genome sizes (36, 37). Several other unique bifunctional
enzymes have been described in Plasmodium species (38-40)
reflecting the parasite’s rapid evolution in its constant fight to
overcome host defence mechanisms.

ACKNOWLEDGMENTS

A.C. was awarded a Predoctoral fellowship by the Comunidad de
Madrid. This research was funded by grants PM1999-0049-CO2-01
and BIO2003-07179 from the Spanish MCYT.

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